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A temperature sensitive escherichia coli mutant defective in dna replication dnaa a new gene adjacent to the dnaa gene



A temperature sensitive escherichia coli mutant defective in dna replication dnaa a new gene adjacent to the dnaa gene



Molecular & General Genetics 178(3): 541-554



An E. coli mutant defective in replication of the chromosome was isolated from temperature-sensitive mutants that cannot support colicin E1 plasmid DNA synthesis in the presence of chloramphenicol. Cellular DNA synthesis of the mutant ceases almost immediately after transfer to nonpermissive temperature. The defect is due to a single mutation, dna-59, which is located close to the sites of dnaA mutations and a couR mutation conferring DNA gyrase with resistance to coumermycin. The dna-59 mutant is not able to support DNA synthesis of .lambda. phage at high temperature. The mutant also restricts growth of .vphi.X174 phage at high temperature, but permits formation of supercoiled closed-circular duplex replicative intermediates. T7 phage can grow on the mutant even at high temperature. A specialized transducing phage .lambda.mm21 [tna dnaA] # 2 supports growth of dna-59, dnaA46 and dna-167 cells at high temperature. Some of the EDTA-resistant derivatives of the phage have lost part or all of the dnaA gene, but carry gene function complementing the defect of dna-59 cells, as judged by conversion of the above dna strains to wild type cells by phage infection and by suppression of the loss of viability of dna-59 cells at high temperature by phage infection. The gene containing the dna-59 mutation site is thus distinct from the dnaA gene. Since the dna-59 mutation does not affect expression of the cour-gene of DNA gyrase, which is another known gene involved in DNA synthesis near the dnaA gene, this mutation is probably in a new gene, dnaN. From analysis of the suppression activities of .lambda.imm21 [tna dnaA] # 2 phage and its deletion derivatives against dnaN59 cells, it is suggested that the expression of the dnaN gene function is reduced by deletion in the dnaA region.

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Accession: 004640118

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PMID: 6248733


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